The present invention is in the field of warning lighting systems for vehicles, and relates more particularly to the activation of one or more warning lights for vehicles in order to alert drivers of following vehicles that the vehicle equipped with the warning lights may be slowing or stopping.
It is quite well known that warning lights at the rear of vehicles, such as automobiles and trucks that are driven on public roads and highways, are essential to alert drivers of other vehicles sharing the same roadways to impending changes in speed and position. Red tail lights are normally used during nighttime hours so that other drivers will see the lighted vehicle; direction signals, also called turn signals, are used to warn other drivers of impending lane change or cornering; stop lights are used, most usually activated by a switch in conjunction with a brake pedal, to warn other drivers that the brakes are being applied.
It is well known, too, that on the public highways many accidents happen because one driver may follow another at a distance that is too close for the following driver to react in time to apply his brakes after he becomes aware, by whatever means, that a vehicle he is following is slowing or stopping. It is also true that accidents happen because one driver may suddenly apply his brakes in the belief that a vehicle ahead is slowing or stopping, when in fact the leading vehicle is not slowing at all, which also might cause a collision. In all states rear warning lights, including stop warning lights, are required by law.
Virtually all wheeled vehicles used on public roads and highways have brakes of some description, such as drum or disk brakes, that act at or on the wheels of the vehicles to bring them to a stop when required. Brakes of this kind typically operate by urging a stationary element against a rotating element, converting the kinetic energy of motion of the vehicle to heat energy through the agency of friction. In virtually all cases, activation of the brakes associated with the wheels of the vehicles, usually by a foot pedal, but in some cases by a hand operated lever or other actuator, causes one or more rear mounted warning lights to light; and when the activating device is released, the lights are turned off.
There are braking systems in use on vehicles operated on public roads and highways other than friction braking devices acting at or on the wheels of the vehicles. Diesel powered tractor-trailer systems, for example, employ devices known as engine brakes, a particular type for example more colloquially known as Jacob's brakes, to slow the tractor-trailer system under varying circumstances. These engine brakes are initiated in various ways, a common method being by an actuator that sends an electrical signal to the engine brake at the engine at an appropriate time. As an example, releasing the accelerator while the transmission is engaged and the engine brake is enabled actuates the signal to engage the engine brake.
Activating the wheel braking system on such vehicles always causes the rear-mounted stop lights to light, and this relationship is required by law to warn following drivers of the immediately impending decceleration of the braking vehicle. Activation of the engine braking system, however, does not light the rear-mounted stop lights, or any other warning light or lights to alert a following driver. This ommission has been the cause of numerous rear-end collisions on the public highways.
The usual combination of events that causes an engine braking system to engage, letting off the accelerator while the transmission is still engaged for example, is a combination that might occur numerous times without perceptible decceleration of a tractor-trailer system, for instance when the driver changes gears. If the stop-lights were activated at each such occurance, following drivers would get erroneous information and might well apply their own brakes and precipitate a dangerous situation. An argument may also be made that allowing the engine braking signal to activate the same warning lights as the wheel brakes would always supply eroneous information, because they are, after all, two different systems causing different deceleration conditions.